1. Field of the Invention
The invention is related to the delivery of submunitions which are the payload of artillery projectiles or missiles that are fired from artillery cannons or launched from aircraft or rocket launchers.
Typically, a large number of these submunitions are carried in a projectile or in a missile in order to cover a large area. These submunitions deliver a shaped charge warhead for armor penetration or fragmentation for antipersonnel application.
The submunitions should be delivered with adequate dispersion, with near vertical angle of descent and have proper fuze function upon impact for maximum effectiveness. If no device is used to retard the flight of the submunitions, they will follow a ballistic trajectory, impact with minimal dispersion and impact at high angle with respect to the vertical.
2. Description of the Prior Art
The retarding device of the prior art causes the submunition to impact with high angles with respect to the vertical and causes a deterioration in the submunition's performance or a complete malfunction or dud ("a complete malfunction" is synonymous to "dud"). If the submunition is not substantially vertical upon impact, the depth of penetration of shaped charge or the distance that the lethal fragments are thrown is significantly decreased.
A second problem of the retarding device of the prior art is that the submunition's fuze is purely mechanical and is dependent on impact angle and ground conditions. The dud rate of a given submunition cluster is increased if the angle of impact varies from the vertical or if the submunition strikes relatively soft medium.
A ribbon loop which is attached to the top of the submunition fuze is one such retarding device. However, this ribbon loop provides only marginal flight stability to the submunition when subject to high spin as with an artillery projectile. With a missile, little or no spin is imparted to the submunition, and consequently the ribbon does not provide sufficient pitch damping. The result is unstable submunition flight and oscillation at very high angles. The looped ribbon does not provide means to drive an alternator for an electronic fuze.
To overcome the problem of a mechanical fuze, a rigid rotor can be used to provide flight stability and torque for driving an alternator, but its application to the aforementioned submunitions has several drawbacks. First, because a rigid rotor is, by its very nature, rigid, it is difficult to pack a rigid wing or rotor in a small oddly-shaped volume. Second, the rigid rotor must be stowed in a non-functioning configuration. Therefore, it requires additional mechanical devices, such as springs and clips, in order to deploy it to its flight configuration. Such additional devices complicate the design, cause reliability problems, and are the source of increased costs and difficulties in loading the submunitions into the carrier. Third, the rigid rotor must be designed to withstand high dynamic loading upon deployment without undergoing permanent deformation. A design of such structural integrity is often quite bulky, increases the overall weight of the projectile, and decreases its effective range. Last, as the rigid rotor is deployed, it assumes an immediate high-drag configuration, i.e. it does not have any intermediate configurations which have a lower drag. This behavior, when coupled with the close proximity of dozens of other deploying submunitions, results in very high probability of failure due to submunition-to-submunition collision.
A rotating parachute (such as a vortex ring or rotafoil) can provide excellent flight stability, i.e. low oscillatory motion upon descent, and can provide a limited amount of torque by using a coupling device such as a clutch. However, the clutch adds cost and adds complication to the system. Additionally, deploying parachutes can be subject to line entanglement as well as collision damage. Thus, the parachute needs to be reefed to allow the staggered filling of the parachute, or it requires some type of protective covering during expulsion/ejection from the carrier and a series of timing devices to release the protective covering at different times to ensure proper submunition cluster deployment. The cost and volumetric penalties, in this case, make the rotating parachute unfeasible.
The performance of rotating parachutes is very sensitive to line length and material dimensional tolerances. This sensitivity along with the difficulties associated with the manufacture of a very small parachute make the rotating parachute an extremely costly alternative.